1. Field of the Invention
The present invention relates to a rotary table device capable of preventing a malfunction of a check valve used therein and preventing penetration of cutting fluid and the like from the outside to the inside of a case.
2. Description of the Related Art
There has been conventionally used a rotary table device shown in FIG. 8, which executes NC control to rotate or divide a workpiece installed on a machining table 3 of a machine tool 1 performing cutting, grinding, electrical discharge machining and the like. This type of device has a rotary table 2 provided with a case equipped with a servomotor, an operation validation switch, an electromagnetic valve, and other electric components, wherein cutting work, grinding work, electric discharge machining and the like are executed on a workpiece attached to the rotary table 2 while spraying/dipping the workpiece with/in cutting fluid, grinding fluid, dielectric working fluid and the like.
Cutting fluid, grinding fluid, and dielectric working fluid may be oil-based or water-soluble. Especially water-soluble fluid is usually sprayed in large amount when cutting a workpiece, in order to remove chips of the workpiece. Moreover, water-soluble cutting fluid, grinding fluid, and dielectric machining fluid are not only higher in permeability than the oil-based ones, but also likely to cause swelling and hardening of the synthetic resin materials used for covering seal packing and cables, deteriorating the resin materials.
Therefore, in the case where a synthetic resin material is used as a sealing member in the rotary table 2 of the machine tool 1, the synthetic resin could deteriorate as time passes, and causes the cutting fluid and the like to penetrate into the case in spite of the airtightness of the case in the beginning. Consequently, the moisture stick to and causes rust on the electric components such as the servomotor, the operation validation switch, and the electromagnetic valve equipped in the case, impairing the insulation properties of the electric components and eventually causing electrical hazards.
Japanese Patent Application Laid-Open No. 11-267939 discloses a rotary table device as the means to solve these problems, in which is provided a check valve that is configured to discharge air only in one direction from the inside of a case of a rotary table to the atmosphere by supplying air into the case and discharging air to the outside of the case when the pressure within the case becomes equal to or greater than a predetermined pressure which is higher than an atmospheric pressure, in order to keep the pressure within the case higher than the atmospheric pressure so that cutting fluid and the like does not penetrate into the case. FIGS. 9 and 10 are each a general view of this rotary table device. Air is supplied from an air supply source 61 connected to an air supply port 51 into a case 55 through an air supply path 57, and the air within the case 55 is discharged to the atmosphere through an air discharge path 59 and a check valve 53.
The technology disclosed in this Japanese Patent Application Laid-Open No. 11-267939 constantly keeps the pressure of the case 55 at a pressure higher than the atmospheric pressure. Such a configuration allows the air to constantly flow in one direction from the inside of the case 55 to the outside through the check valve 53. As a result of this air flow in one direction, the check valve 53 assumes a state in which the valve thereof is opened for the long time, whereby the O-ring and the like on the check valve 53 becomes fixedly attached to a sliding portion, making it difficult for the check valve 53 to return even when the pressure inside the case 55 drops.
When the air inside the case 55 is leaked to the outside or when the air is no longer supplied to the case 55 due to deterioration of a sealing member of the case on account of the cutting fluid and the like, the pressure inside the case 55 cannot be kept at a pressure higher than the atmospheric pressure, causing penetration of the cutting fluid and the like from the check valve 53 into the case.